STANHOPE, CHARLES, third Earl Stanhope (1753–1816), politician and man of science, born in London on 3 Aug. 1753, was the second but eldest surviving son of Philip, second earl Stanhope (d. 7 March 1786), who married, in 1745, Grizel (d. 1811), daughter of Charles Hamilton, (by courtesy) lord Binning [q. v.], and sister of Thomas, seventh earl of Haddington. The father, the second earl Stanhope, was son of James Stanhope, first earl Stanhope [q. v.] Educated at Utrecht and Geneva, he acquired a love for mathematics, for the Greek language—which was as familiar to him as English—and for democratic principles. Lalande called him the best English mathematician of his day, and he was an especial friend and correspondent of Robert Simson [q. v.], the professor of mathematics at Glasgow. He paid for the posthumous impression of Simson's works and for the edition of the works of Archimedes that was printed at the Clarendon Press, and Priestley dedicated to him the third volume of his ' Experiments on Air.' In 1735 he was elected F.R.S., and at his death he left 500 l. to that society (Weld, Royal Society, ii. 196). In parliament he spoke, while in England, not infrequently, and always with independence of thought. Letters of Pitt, Lord Chatham, and Franklin to him, and one from him are in the 'Chatham Correspondence' (vol. iv.) He transmitted to his son Charles his enthusiasm for science, his devotion to the cause of democracy, and his fondness for simplicity in dress (Mahon, Hist. of England, iii. 208-9).

Charles was sent to Eton at an early age. It is usually said that he went thither at the age of eight, but his name is not in the list of 1762 (Collect. Oxford Hist. Soc. iii. 367). His elder brother Philip died at Geneva on 6 July 1763 (Gent. Mag. 1763, p. 415), and Charles became Lord Mahon and the heir to the peerage. In July 1764 the whole family went to Geneva (Letters of Lady Hervey, pp. 303, 309), where the lad was instructed by G. J. Le Sage, who developed his tastes for the exacter sciences. He also spent much time in experimental philosophy. In 1765 he had the advantage for two months of the society of Adam Smith and of Henry Scott, third duke of Buccleuch [q. v.] (Dugald Stewart, Works, x. 45). Lady Mary Coke was at Geneva in October 1769, and marvelled at the youth's 'surprising genius; his painting wou'd surprise you, and he cuts out people in paper as like as others can draw them. He has invented a mathematical instrument … better for the purpose it is intended than any other of the kind; yet he is but seventeen years of age' (Journal, iii. 158). Still he did not neglect the amusements of youth. He excelled in horsemanship, enrolled himself in the militia of the Genevan republic, and was an adept in shooting at a mark.

At the age of eighteen Mahon composed a paper in French on the pendulum, which the Academy of Stockholm rewarded with a prize and printed. He wrote, at Geneva in 1773, a volume, printed in 1775, of 'Considerations on the Means of preventing Fraudulent Practices on the Gold Coin.' The coin was to have very little relief, and the date was to be sunk in. The dangers to be guarded against were false coining, clipping, milling, and sweating. Very soon after its composition the Stanhopes returned to England, and Mahon threw himself with ardour into politics.

Early in September 1774 he was presented at court, and as his father would not allow him to wear powder 'because wheat is so dear,' he went in his natural 'coal-black hair' and a white feather. The wits said 'he had been tarred and feathered' (Walpole, Letters, vi. 114). A few weeks later, when only just of age, he contested the city of Westminster, but, after the poll had been open for some days, withdrew. At this time he was inspired with an ardent friendship for the second William Pitt, who was then equally ardent for reform, and their alliance was cemented by his marriage, on 19 Dec. 1774, to his friend's sister, Lady Hester Pitt, elder daughter of the first Earl of Chatham. Lady Mahon died at the family seat of Chevening, Kent, on 18 July 1780, when only twenty-five.

During the Gordon riots of June 1780 Mahon harangued the people from the balcony of a coffee-house, and urged them to retire to their homes. Walpole said that he 'chiefly contributed by his harangues to conjure down the tempest' (Letters, vii. 377-81). On the following 6 Sept. he was elected, through the influence of the Earl of Shelburne, member for the borough of Chipping Wycombe in Buckinghamshire, and represented it until his accession to the peerage. At the opening debate (October 1780) on the choice of speaker, he made his maiden speech, and in 1781 he was a delegate for the county of Kent to advocate the cessation of the American war and the promotion of parliamentary reform. From 1782 to 1786 he introduced into the House of Commons several bills for the prevention of bribery and corruption and for the reduction of expenses at parliamentary elections. The provisions of his bill against bribery were declared by Lord Mansfield on 23 March 1784 to be already part of the law of the land (Gent. Mag. 1784 i. 229). His bill for annual registration of voters, for increase in the number of polling places, and for other improvements at elections was taken charge of after he had become a peer by Wilberforce, and, with Pitt as its friend, passed the commons, but was thrown out by the lords on 5 July 1786.

Mahon had associated himself with the whigs in their opposition to the war with the American colonies, but he strongly opposed the coalition of Fox and North, and he was vehement against Fox's East India Bill. He declined office on the formation of Pitt's cabinet in 1783, but remained for a short time his strenuous supporter. At the general election in 1784 he laboured in the interest of Pitt. Walpole at the time dubbed him 'a savage, a republican, a royalist I don't know what not' (Letters, viii. 469). He spoke at the meetings of the electors of Westminster in February 1784 against Fox and the coalition (cf. Jephson, The Platform, i. 155-6). His first political difference with Pitt took place on 22 July 1784 over the tax on bricks and tiles. He ridiculed the arguments of George Rose (1744-1818) [q.v.] in its favour, and Pitt rallied him ironically in return.

On 7 March 1786 he succeeded to the peerage as the third Earl Stanhope, and lost no time in attacking by speech and pamphlet Pitt's proposals for a sinking fund. His pamphlet was entitled 'Observations on Mr. Pitt's Plan for the Reduction of the National Debt,' and Pitt tried hard to dissuade him from its publication (Lord Auckland, Journal, i. 369). Two bills were introduced by him into the House of Lords in the summer of 1789. One was for relieving members of the church of England from sundry penalties and disabilities; the other was for preventing vexatious proceedings for the recovery of tithes. Both were thrown out, the first on 18 May, the second on 3 July, and on the first date he created much amusement by informing the lord chancellor that 'on another occasion I shall teach the noble and learned lord law, as I have this day taught the bench of bishops religion.' He was accordingly represented in caricature as a schoolmaster, with a rod in his hand. His speeches abounded in pithy expressions and in illustrative anecdote, although his gesture was ungraceful.

Up to this date Stanhope had remained on friendly terms with William Pitt, but differences over the French revolution led to their permanent estrangement (Stanhope, Pitt, ii. 180-1). He was chairman of the 'Revolution Society,' which was founded in 1788 to commemorate the centenary of the English revolution of 1688, and he forwarded to Paris the address of congratulation on the capture of the Bastille, which had been moved at its meeting on 4 Nov. 1789 by Dr. Price. To Rochefoucault he sent the resolution of congratulation on the establishment of liberty in France, which was proposed by Sheridan at a meeting held at the Crown and Anchor tavern in the Strand on 14 July 1790. It was read in the assembly on 21 July, and circulated in French. Letters sent by him to Condorcet were printed at Paris in 1791 and 1792, the first set arguing against the issue of false assignats, and the second relating to the treatment of negroes. He published in 1790 'A Letter to Burke, containing a Short Answer to his Late Speech on the French Revolution,' which went into a second edition and was translated into French in that year. Mrs. Macaulay addressed to Stanhope her 'Observations on the Reflections of Mr. Burke on the Revolution in France.'

Stanhope, during 1791 and 1792, supported Fox's libel bill for maintaining the rights of juries, and published his arguments with a catena of legal authorities in their support. By letter to Lord Grenville, with whom he was still on friendly terms, and by speeches in parliament, he consistently opposed the war with France. On 23 Jan. 1794 he moved to acknowledge the French republic, and on 4 April 1794 he brought forward a motion 'against any interference in the internal government of France,' which provoked his fellow-peers, at Lord Grenville's instance, to order the entry of it to be expunged from their journals. Both of these speeches were printed separately. Next month he opposed the Habeas Corpus Suspension Bill, and on 6 Jan. 1795 he introduced a second motion against interfering with the internal affairs of France. On this occasion he was 'in a minority of one,' and after entering a protest against the defeat of his motion, which he subsequently published, he withdrew from further attendance in parliament. A medal was struck in his honour with the motto 'The minority of one, 1795,' and he was long known by that title or as 'Citizen' Stanhope. From 1791 to 1808 he was a frequent figure in the caricatures of Gillray. One satiric print was entitled 'Scientific Researches, New Discoveries in Pneumatics.' When he declared himself a sans-culotte, a ballad, with a rough caricature of him by another satirist, was scattered broadcast.

Owing to his revolutionary sympathies, Stanhope's house in Mansfield Street was attacked by rioters and set on fire at different times on the night of 11-12 June 1794. He believed, and declared in an advertisement, that the mob had been paid. The Rev. Jeremiah Joyce [q.v.], his private secretary and the tutor to his sons, was on 4 May 1794 arrested at Chevening on a charge of 'treasonable practices.' To celebrate his acquittal Stanhope on 23 Dec. 1794 gave a grand entertainment at Chevening to his neighbours and tenants (Gent. Mag. 1795, i. 73). At a very large meeting at the Crown and Anchor tavern on 4 Feb. 1795, in honour of the acquittal, he was called to the chair and delivered an animated speech, which, when published, enjoyed great popularity. In this year of 1795 Walter Savage Landor printed anonymously 'A Moral Epistle to Earl Stanhope,' a poem of twenty pages, which contrasted him with Pitt, much to the commoner's disadvantage (Foster, Landor, i. 68-71).

Stanhope's secession from the House of Lords lasted from 6 Jan. 1795 to 20 Feb. 1800. In the beginning of 1799 he addressed to the people of Great Britain and Ireland a pamphlet 'On the Subject of an Union,' which was reprinted and circulated by the anti-union party of Dublin. His first motion on reappearing among the peers was to propose a peace with Napoleon; but he acted without concert, and only one peer, Lord Camelford, supported him. In 1808 he took a very strong part against the Indictment Bill, as interfering with the liberty of the subject, and at all times spoke strongly against the slave trade. He advocated a reduction of fiscal duties as tending to an increase in the revenue, and was earnest for education on a comprehensive basis. On 27 June 1811 he introduced a 'gold coin and bank-note' bill, making it illegal to pay a larger sum than 21s. for a guinea, and for preventing any note issued by the Bank of England from being accepted at a discount. It passed through both houses. In the last year of his life he carried through the lords two motions for the appointment of committees one for a revision of the statute-book, and the other for the adoption of a uniform system of weights and measures.

Throughout his life Stanhope deservedly enjoyed a great reputation for his discoveries in science, to the prosecution of which he devoted much time and money. He was elected F.R.S. on 19 Nov. 1772, but through absence from England was not admitted until 12 Jan. 1775 (Records of Royal Soc.), and he was a member of the Philadelphia Philosophical Society. It is believed that Richard Varley, father of John Varley [q. v.] the artist, was his tutor in mechanics. His principal experiments related to the safeguarding of buildings against fire by means of 'stucco,' in which he endeavoured to bring to perfection the plans of David Hartley the younger [q. v.] He took out patents for steam-vessels in March and August 1790, and in February 1807. It was announced in the 'Gentleman's Magazine' for 1792 (ii. 956) that his experiments for propelling vessels by the steam-engine without masts or sails had been so satisfactory that a ship of two hundred tons was being built under his direction on this principle. His inventions received the approval of the lords of the admiralty in 1795 and 1796. An 'ambi-navigator' ship called the Kent was constructed for him, but did not turn out a success (Stanhope, Pitt, 11. 397-401). In 1795 the earl revived the project of Genevois, the pastor of Berne, for impelling boats with duck-feet oars, but the highest rate of speed attained was three miles an hour (cf Whitaker, Course of Hannibal, 1794,ii. 142; Mathias, Shade of Pope, 1799). Stanhope declared in the House of Lords on 21 May 1810 that he had invented 'a vessel 111 feet in length which drew only seven feet odd inches of water, and outsailed the swiftest vessel in the navy.' His specification 'respecting ships and vessels' was printed in 1807.

Many printing appliances devised by himself he placed at the public disposal, without any advantage to himself, and made solid contributions to the art of printing. His chief assistant in this department of mechanics was Robert Walker, an ingenious mechanician of Vine Street, Piccadilly, and Dean Street, Soho. He perfected a process of stereotyping which was acquired by the delegates of the Clarendon Press at Oxford in 1805 on the condition that they paid 4,000l. to the foreman and manager of his press, Andrew Wilson, of Wild Court, and stereotyping on this system became part of the general business of the press. They also acquired, but free from any payment, his iron hand-press, called the Stanhope press, and his system of logotypes and logotype cases. This system a few years later was introduced into the Oxford press; but his logotypes, like those of John Walter [q. v.] of the 'Times,' proved a failure. The first book printed by his process was 'An Abstract of the whole Doctrine of the Christian Religion. By J. A. Freylinghausen,' 1804. Long after these dates he persevered with his experiments, either at Wilson's office or at Chevening, where he kept a foundry of his own. Another invention he called 'pantatype printing, by which one hundred thousand impressions of an engraving could be taken, all proofs; that is to say, the last impression will be as perfect as the first '(Collectanea, Oxford Hist. Soc. 1896, iii. 365-412; Hansard, Typogmphia, p. 475; H. G. Bohn on Printing, Philebiblon Soc. iv. 90).

Stanhope published in 1806 his 'Principles of the Science of Tuning Instruments with Fixed Tones,' which was reprinted in Tilloch's 'Philosophical Magazine' (xxv. 291-312). The invention formed the subject of numerous articles by John Farey and Stanhope in that magazine, and of Dr. Callcott's 'Plain Statement of Earl Stanhope's Temperament.' In 1779 he produced his 'Principles of Electricity,' but a second volume which he promised, in refutation of the conclusions drawn from the experiments of Benjamin Wilson, was not published. In the first volume and in the 'Philosophical Transactions' (lxxvii. 130) he contended that when a large cloud is charged with electricity it drives out a considerable portion of the electricity in its neighbourhood, which often returns to its original position with such violence and in such quantity as to destroy life. In this way he explained the death of a carrier and his horses at Berwickshire in 1787, though there was no discharge of thunder nearer than some miles distance (Thomson, Royal Soc. pp. 449-50). A public trial of Franklin's and Stanhope's experiments in lighting-conductors is said to have taken place at the Pantheon under the superintendence of Edward Xairne the electrician.

About 1777 Stanhope constructed two calculating machines (1) for working out with exactness complicated sums of addition and subtraction; (2) for similar sums in multiplication and division. 'The Stanhope Demonstrator, an Instrument for performing Logical Operations,' employed his thoughts at intervals for thirty years. It has been fully described by the Rev. Robert Harley, F.R.S., in an article in 'Mind' (iv. 192-210), which was reprinted separately for private circulation.

Stanhope's other inventions include a microscopic lens which, like the printing-press, bears his name; a new manner of producing cement more durable than the ordinary mortar; an improved method of 'burning chalk, marble, and limestone into lime; 'an artificial slate or tile for excluding rain and snow; and a means of curing wounds made in trees. In conjunction with Robert Fulton, the American engineer, he projected a canal from his estate at Holsworthy in Devonshire to the Bristol Channel, with a novel system of inclined planes and with improved locks.

Stanhope's life was thus one of unremitting toil. He died of dropsy at Chevening, on 15 Dec. 1816, and was buried with marked simplicity in the family vault at that church on 24 Dec. In person he was tall and thin, with a high forehead and a countenance expressive of impetuosity. He was always very plain in his attire, and of late years his looks were pale and wan. A powerful voice and a vigorous gesticulation heightened the effect of his oratory. His sympathies were wide, his generosity was unbounded, and his views were much in advance of their time. In all that he did whether it was in politics or in science, he worked for the public good. The defects of his character were an incapacity to work with others and a lack of sympathy towards his children, all of whom he disinherited after subjecting them to much ill-treatment. But Stanhope's mother left everything to her 'dearly beloved son, Charles, Earl Stanhope, from my approbation of his private and public conduct' (Gent. Mag. 1812, i. 673). By his will, made in 1805, Stanhope left all his disposable estate, after payment of a few legacies, among ten executors, of whom the best known were Lord Holland, Lord Grantley, Joseph Jekyll, George Dyer, and the Rev. Christopher Wyvill.

Stanhope married as his second wife, on 12 March 1781, Louisa, only daughter and sole heiress of the Hon. Henry Grenville, younger brother of Earl Temple and George Grenville. She died at Clarges Street, Piccadilly, on 7 March 1829, aged 70. By his first wife he had three daughters: (1) Hester Lucy Stanhope [q. v.]; (2) Griselda, who married at Marylebone church, on 29 Aug. 1800, John Tekell, of Hambledon, Hampshire; she died without issue, at Bagshot, on 13 Oct. 1851, aged 73 (Gent. Mag. 1851, ii. 667); and (3) Lucy Rachael, who eloped early in 1796 with Thomas Taylor of Sevenoaks, the family apothecary. Stanhope's resentment at this marriage exposed him to one of Gillray's most pungent satires, 'Democratic Levelling: Alliance à la Française; or the Union of the Coronet and Clyster-pipe,' 4 March 1796. Pitt requested Taylor to abandon his business, and made him controller-general of the customs. Lord Chatham made Taylor's eldest son, William Stanhope Taylor, one of his executors, and he edited with Pringle the volumes of the 'Chatham Correspondence.' Lady Lucy Taylor died at Coldharbour, Surrey, on 1 March 1814, when a pension of 100l. per annum was granted to each of her three sons and four daughters.

By his second wife Stanhope left three sons. Philip Henry, the eldest son, succeeded to the peerage [see under Stanhope, Philip Henry, fifth Earl], Charles Banks (1785-1809), the second son, was killed at Coruña. James Hamilton (1788–1825), the third son, was captain and lieutenant-colonel of the 1st foot-guards.

A three-quarter length portrait of Stanhope by Gainsborough, left unfinished through the death of the artist, is preserved at Chevening. The first adequate reproduction is in the third volume of the 'Collectanea' of the Oxford Historical Society. A portrait of Stanhope by Opie, bequeathed to Lord Holland, is in the journal-room at Holland House (Rogers, Opie and his Works, p. 165). A profile, drawn from the life and engraved by Henry Richter, was published on 4 June 1798. Another likeness, drawn and engraved by C. Warren, appeared in the 'Senator' in 1792. A number of private papers, referring chiefly to his inventions, are preserved at Chevening.